Answer:
3/4
Explanation:
The 0 <= theta <= pi/2 makes it so the angle must be in the first quadrant. From there, you can use the fact that sin = opposite / hypotenuse.
Thus the opposite side length would be 5, the hypotenuse would be 5, and the adjacent side length would be 3 (by Pythagorean theorem).
Recall that cot = cotangent = 1 / tan. And recall that tan is opposite of adjacent. So tan(theta) = 4/3, and cot (theta) = 3/4.